Parallel connected tap changers employing simultaneously movable contacts

ABSTRACT

A pair of mechanical tap changers supply current to a load from pairs of transformer taps having like voltages. Corresponding stationary contacts of the tap changers are simultaneously coupled to transformer taps having identical voltages, and current is supplied to the load from the center tap of a limiting reactor connected between the output terminals of the tap changers. Actuation of the tap changers is synchronized by means of a chain drive coupling the movable elements of the tap changers.

United States Patent Robert 11. Brennan Plttsfleld, Mass. 2

Mar; 19, 1970 Nov. 9, 197 1 General Electric Company [72] Inventor [211 App]. No. [22] Filed [45] Patented [73] Assignee [54] PARALLEL CONNECTED TAP CHANGERS EMPLOYING SIMULTANEOUSLY MOVABLE CONTACTS 4 Claims, 2 Drawing Figs. [52] U.S. Cl. 323/435 R [51] Int. Cl ll02p 13/06, G05f 1/14 [50] Field of Search 323/435 R, 91; 336/150 [56] References Clted UNITED STATES PATENTS 2,434,503 1/1948 McCarty 323/435 R 4/1954 Aicher 2,675,519 323/435 R 2,712,110 6/1955 Peterson..... 323/435 R 3,421,073 1/1969 Perkins 323/435 R Primary Examiner-Gerald Goldberg Attorneys-Francis X. Doyle, Vale P. Myles, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT: A pair of mechanical tap changers supply current to a load from pairs of transformer taps having like voltages. Corresponding stationary contacts of the tap changers are simultaneously coupled to transformer taps having identical voltages, and current is supplied to the load from the center tap of a limiting reactor connected between the output terminals of the tap changers. Actuation of the tap changers is synchronized by means of a chain drive coupling the movable elements of the tap changers.

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PARALLEL CONNECTED TAP CHANGERS EMPLOYING SIMULTANEOUSLY MOVABLE CONTACTS BACKGROUND OF THE INVENTION The present invention relates to voltage magnitude control systems, and more particularly to a tap-changing system for a step-type voltage regulator wherein a plurality of transformer output taps are selectively engaged by a movable contactor.

With the increased use of electric and electronic equipment in modern industrial processes, closely regulated voltage supplies have become essential. Along with the increased need for efficiency and accuracy in voltage regulation has come the equally important demand for economical means of providing such regulation. One common means for providing voltage regulation comprises a step-type voltage regulator and an associated transformer. The secondary winding of a transformer is divided into a plurality of tap sections, each successive tap providing an incrementally differing output voltage. The taps are coupled to a group of stationary contacts of the step-type regulator which are disposed in a circular arrangement, and which are sequentially engaged by rotatable fingers which conduct the desired voltage toan output terminal. As power requirements have increased, the current capacity and thus the physical size of the regulator has similarly increased. Further, as voltage regulator capacities have increased, builders of such equipment have been faced with the ever-increasing problem of arcing between the movable and stationary contacts. In the past, when high k.v.a. capacities have been required, it has been necessary to provide a separate switch, or contactor, in addition to the above-described tap-changing device. In such prior art apparatus, the contactor first opens, interrupting the flow of current to the tap changer, the tap changer fingers are rotated to engage a new stationary contact providing the desired voltage, and the contactor is closed. Ordinarily, such contactor takes the form of a heavy electromechanical switch, although vacuum switches are also utilized. In such apparatus, it is necessary to incorporate into the voltage regulator a mechanism which provides for the proper sequence of operation, i.e., a sequencing device which must first open the contactor before allowing the tap-changing mechanism to move, operate the tap changer, and finally reclose the contactor. Such mechanisms, whether they are mechanical, electromechanical, or electronic, necessarily add to the complexity and expense of the voltage regulating system.

SUMMARY OF THE INVENTION The present invention contemplates the elimination of the aforementioned contactors, and the sequencing equipment found in the prior art voltage regulating systems. Rather than providing a single tap changer whose contacts must withstand destructively high k.v.a. requirements, the instant invention utilizes two or more low-current capacity tap changes connected in parallel. The stationary contacts of the tap changers may be coupled to common taps on a single transformer winding; or a plurality of smaller transformers may be used, each one having output taps connected to a separate tap changer. By dividing the load current among several tap changers the current flowing through the contacts of each changer, and thus the arcing supported thereby, is brought within acceptable limits. However, should one tap changer operate before the other, the contacts of the last operated unit would then be called upon to withstand a disproportionately high load current. Further, a voltage differential would then occur between the two units, causing undesirable circulating currents in the tap changers and associated transformer windings.

To preclude the occurrence of this condition, the tap changers are positively linked together, as by means of a chain and sprocket arrangement although other means may be utilized. In addition, to mitigate any slight voltage imbalance or transient currents which might result from the switching, and to limit current flow shouldone of the tap changers develop a short circuit or other electrical fault, a center tapped current limiting reactor is connected between the output terminals of the tap changers. Load current is then drawn from the center tap of the limiting reactors.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic circuit diagram of a step-type voltage regulator embodying the principles of the subject invention.

FIG. 2 is a schematic circuit diagram of a further embodiment of the subject invention wherein voltage is obtained from a single transformer winding.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a pair of transformers T, and T, whose secondary windings are divided into a plurality of tap sections. The taps are each connected to one of a plurality of circularly located stationary contacts 10,-10, and l2,,l2 of a pair of tap changers generally indicated at 10 and 12. The tap changers l0 and 12 are identical, and corresponding stationary contacts of each changer are connected to transformer taps of transformers T, and T which provide similar voltages. The tap windings of the transformer may be energized by a common primary winding, or alternatively, the transformers T, and T, may be separate transformers, both of which are coupled to a common voltage source. The movable switching elements of tap changers l0 and 12 ordinarily take the form of a pair of radially extending fingers l4, l6 and I8, 20, respectively, which are spaced far enough apart to bridge the gap between consecutive stationary contacts, but close enough to lie upon the same stationary contact, if desired. Fingers l4, l6 and I8, 20 respectively, are physically separated from one another, but are electrically connected through center-tapped, limiting reactors 22 and 24. Current output from tap changers l0 and 12 thus flows from center taps 26 and 28 of limiting reactors 22 and 24. The center taps 26 and 28 are connected through a third limiting reactor 30 which is provided with a center-tapped output terminal 32 for supplying current to a load connected between terminals 32 and 34. The rotatable, radially extending fingers I4, 16 of tap changer 10 are operated by shaft 36 connected to geneva gear 38, while the rotatable, radially extending fingers I8, 20 of tap changer 12 are operated by shaft 40 connected to geneva gear 42. Each geneva gear 38, 42 is driven by a motor 44, 46 through a gear train 48, 50 (only gear train 50 being shown as such) in a manner well understood by those skilled in this art. As shown, each geneva gear 38, 42 is operated by means of shaft 52, 54, respectively, which is actuated through the gear train 48, 50. In order to synchronize the tap changers 10 and I2, sprockets 56, 58 are provided on shafts 52, 54, respectively. A drive chain 60 couples sprockets 56, 58, as shown, to keep the tap changers l0 and 12 in step or synchronism. As is understood, control means 62, 64 energize motors 44, 46 to operate tap changers l0 and 12.

The operation of the voltage regulator of FIG. 1 will now be described. When transformers T, and 'I,are energized, incremental voltages will exist between the taps of the output windings thereof, and thus between the stationary contacts of the tap changers to which the taps are connected. Should both fingers of a tap changer rest on a common stationary contact, no voltage differential will exist between them, and each will transmit an equal amount of current to the current-limiting reactor and thus to the center tap output terminal. The voltage provided at the center tap of a limiting reactor in the configu ration just described is thus that of the winding tap to which the fingers are coupled. As the fingers are rotated, the leading finger breaks contact with the stationary contact, and the full current supplied by the changer flows through the trailing finger. Upon further rotation of the fingers, the leading finger encounters the next stationary contact. The full differential voltage between the consecutive contacts is thus impressed across the balancing reactor connecting the fingers. A circulating current now occurs which traverses that segment of the transfon'ner winding lying between the two taps bridged by the fingers, and the limiting reactor winding. However, due to the opposite fluxes which it induces in the reactor winding, the circulating current is substantially attenuated. The load current, however, traverses the equalizing reactor, without encountering substantial impedance and flows to the load. Further movement of the fingers brings the trailing finger into contact with the same stationary segment upon which the leading finger rests.

The foregoing description holds true for all tap changers of the type described. In the disclosed embodiment, tap changers and 12 operate in the described manner, each supplying current to a load from a separate transformer winding. The gear train 418 of tap changer 10 driven by motor 414, is mechanically coupled to gear train 50 of tap changer 12, which is driven by motor 46 by means of a drive chain 60. The drive chain 60 forces the shafts 36, 410 to move simultaneously so that the fingers of the two tap changers 10 and 12 are rotated at substantially the same instant. Thus, should the fingers of tap changer 10 both lie upon stationary contact 10,, for example, the fingers of tap changer 12 would be constrained to lie upon corresponding stationary contact 12,. Since the stationary contacts 10f and 12f are coupled to corresponding output taps of transformers T and T substantially identical voltages appear at center taps 26 and 28 of balancing reactors 22 and 24.

The best coupling mechanism will generally not provide perfect synchronism. Further, while the voltages at corresponding taps of similar transformers are theoretically identical, production tolerances, differences in materials, and other variations may cause some voltage imbalance to be present. It has been found that if a third limiting reactor 30 is connected between the outputs of balancing reactors 22 and 241, and load current is taken from the center tap 32 the foregoing problems are substantially reduced. Should the voltage at output 26 of tap changer 10 momentarily difi'er from that of output 28 of tap changer 12, the circulating current caused thereby will be substantially limited by reactor 30.

FIG. 2 is a further embodiment of the subject invention wherein a single transformer winding generally indicated at T is divided into a plurality of tap segments. Each tap is connected to corresponding stationary contacts 110 -110, and 112,,-112, of tap changers 110 and 112, respectively. The fingers 114 and 116 of tap changer 110 and fingers 118 and 120 of tap changer 112 are affixed to rotatable shafts 136 and 140 driven by geneva gears 138 and 142, respectively. Sprockets 156 and 158 are mounted on the input shafts 152 and 154 of gear drives 148 and 150, respectively. Chain 160 driveably connects the sprockets, thus mechanically synchronizing the operation of the movable elements of the two tap changers 110 and 112.

As with the circuit of FIG. 1, first and second limiting reactors 122 and 1241 are connected between the fingers of the movable contactors of each of tap changers 110 and 112, and a third limiting reactor 130 having a center-tapped output terminal 132 is coupled between the center-tapped outputs 126 and 128 of reactors 122 and 124, respectively. Circulating current resulting from any slight misalignment or lack of synchronization between corresponding fingers of tap changers 1110 and 112 is thus minimized due to the presence of reactor 130.

Although load current is drawn from common transformer taps, each tap changer still conducts only one-half of the load current. Similarly, the windings of limiting reactors 122 and 124 each transmit only one-half of the current drawn by the load. As the embodiment of FIG. 1, balancing reactor 130 carries full load current. The load sustained by the contacts of each of the tap changers is thus drastically reduced, providing increased life and lessened expense in that much smaller tap changers may be utilized than would be the case if a single tap changer were called upon to carry full load current.

From the above it will be clear that by means of this invention there is provided a voltage regulator whose tap-changing elements each carry only a fraction of full load current, yet WhlCh provides for the rapid, efficrent switching of step-type transformers. It will be understood by those skilled in the art that, while the forms of the invention herein shown and described constitute preferred embodiments of the invention, it is not intended herein to illustrate all of the possible equivalent forms or modifications of the invention. For example, it may be desirable to provide four or more paralleled tap changers, all of which are mechanically synchronized by either the method shown herein or other suitable means know in the art. Various changes may thus be made without departing from the spirit or scope of the invention herein disclosed, and it is intended that the appended claims cover all such changes as fall within the true spirit and scope of the invention.

What is claimed as new and what is desired to Letters Patent of the United States is:

1. A voltage regulator comprising:

a plurality of transformer means, each having a winding divided into tap segments by a plurality of output taps thereon;

a plurality of switching means each having a plurality of stationary contacts, each of said stationary contacts of said switching means being coupled to a different one of said output taps, each of said switching means further having movable contact means for successively engaging the stationary contacts thereof;

current-limiting means connecting the movable contact means of predetermined pairs of said switching means; and

means mechanically connecting all of said movable contact means of said switching means for causing said movable contact means to substantially simultaneously engage stationary contacts of each of said switching means.

2. A voltage regulator, comprising:

first and second transformer windings, each of said windings being divided into segments by a plurality of taps, corresponding taps of each of said winding being at like voltages;

first and second switching means, each of said switching means having a plurality of stationary contacts, each of said contacts being connected to a different tap, the contacts of said first switching means being connected to the taps of said first transformer winding and the contacts of said second switching means being connected to the taps of said second transformer winding;

said first and said second switching means further having movable contacts for successively engaging said stationary contacts;

current-limiting means connected between the movable contacts of said first and said second switching means, said current-limiting means having a tap thereon for providing an output voltage; and

means connecting said movable contacts of said first and second switching means for causing said switching means to simultaneously be corresponding taps of said first ans said second transformer windings.

3. A voltage regulator as defined in claim 2, wherein said means connecting said movable contacts comprises a chain and sprocket drive.

4. A voltage regulator as defined in claim 2, wherein the movable contacts of each of said switching means comprise first and second fingers, said fingers having current-limiting means electrically connected therebetween.

a 4 a W be secured by UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 19,? Dated November 9, 1971 Inventor(s) Robert H. Brennan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

CO1 2, line 18 "l2 -l2" should be l2 -l2 Col. 4, line 1 know" should be known Col. L, line 60 After "be" insert connected to Col. l line 60 After "first" 'ans' should be and Signed and sealed this 9th day of May 1972 (SEAL) Attest:

EDWARD M.FLETCEDER,JF3.

F1 1 NF 1 A mestipg Offj C9? B1 GOFIJLHALK Commissioner of Patents 

1. A voltage regulator comprising: a plurality of transformer means, each having a winding divided into tap segments by a plurality of output taps thereon; a plurality of switching means each having a plurality of stationary contacts, each of said stationary contacts of said switching means being coupled to a different one of said output taps, each of said switching means further having movable contact means for successively engaging the stationary contacts thereof; current-limiting means connecting the movable contact means of predetermined pairs of said switching means; and means mechanically connecting all of said movable contact means of said switching means for causing said movable contact means to substantially simultaneously engage stationary contacts of each of said switching means.
 2. A voltage regulator, comprising: first and second transformer windings, each of said windings being divided into segments by a plurality of taps, corresponding taps of each of said windings being at like voltages; first and second switching means, each of said switching means having a plurality of stationary contacts, each of said contacts being connected to a different tap, the contacts of said first switching means being connected to the taps of said first transformer winding and the contacts of said seconD switching means being connected to the taps of said second transformer winding; said first and said second switching means further having movable contacts for successively engaging said stationary contacts; current-limiting means connected between the movable contacts of said first and said second switching means, said current-limiting means having a tap thereon for providing an output voltage; and means connecting said movable contacts of said first and second switching means for causing said switching means to simultaneously be connected to corresponding taps of said first and said second transformer windings.
 3. A voltage regulator as defined in claim 2, wherein said means connecting said movable contacts comprises a chain and sprocket drive.
 4. A voltage regulator as defined in claim 2, wherein the movable contacts of each of said switching means comprise first and second fingers, said fingers having current-limiting means electrically connected therebetween. 